Electric flow-through water heaters are commonly utilized to heat circulating water for use with a spa/hot tub and other such applications. Electric flow-through water heaters commonly employ an electrical heating element disposed in a metallic vessel such that the heating element is in contact with the flow of water to provide heat exchange to the water as it flows along the heating element. In addition, a water pump is generally used to continuously circulate water through the heater vessel. In the conventional water heating systems, a thermostat is typically disposed within the hollow of the vessel to sense the temperature of the heated water, and the heating element is generally controlled based on the sensed water temperature. According to many conventional approaches, the electric heater is controlled in response to the sensed temperature of the water to maintain a desired water temperature.
Modern pools, spas and the like may utilize a variety of chemicals in the water to prevent growth of bacteria or other undesirable organisms. Such chemicals may be highly reactive/corrosive, thus limiting the life of the heater element when exposed to the water and chemicals. Although stainless steel is corrosion resistant, the highly reactive nature of the chemicals degrades even known stainless steel heater elements. Known heater elements include a tubular stainless steel outer jacket with an inner conductive wire extending through the outer jacket. A dielectric insulation such as magnesium oxide or other suitable dielectric medium is disposed around the inner conductive wire to permit transfer of heat from the inner conductive wire to the outer jacket, while providing electrical insulation between the inner conductive wire and the outer jacket. The magnesium oxide or other powder is packed tightly to promote heat conduction from the inner conductive wire to the stainless outer jacket. In an attempt to alleviate the corrosion problems caused by the water and corrosive chemicals, a titanium outer sleeve material has been tried. However, the high temperatures of the heating element cause the titanium to stress relieve, thus significantly reducing the compaction and heat conduction capability of the magnesium oxide.
One type of known water heater includes a generally cylindrical hollow vessel that may be made of a metal or polymer material. An electrical heating element is disposed within the housing, with opposite ends of the heating element extending through the sidewall of the housing to provide an electrical connection to the heating element. If the hollow vessel is made of a metal material that is the same as the electric heating element, the electric heating element may be welded to the vessel where the heating element passes through the sidewall. However, such welding operations may be difficult and/or expensive particularly if the vessel and heating element are made of a dissimilar material. Alternately, another known arrangement is illustrated in U.S. Pat. No. 6,080,973. This heater arrangement includes a hollow vessel that is made of a polymeric material, and compression fittings are utilized to seal the joint between the electrical heating element and the hollow vessel. This arrangement utilizes metal support members that position the heating element within the vessel to prevent the heating element from contacting and damaging the polymeric walls of the vessel.
Thus, a heater alleviating the problems associated with existing water heaters would be desirable.
One aspect of the present invention is a spa system including a tub having a sufficient size to accommodate an adult human. The spa system includes a powered pump, an electrical heater, and a tubing system interconnecting the tub, pump, and electric heater to provide recirculating flow of water through the spa system. The electrical heater includes a housing made of a polymer material and defining an internal passageway adapted for fluid flow through the housing. The housing has a first opening in fluid communication with the passageway, and a pair of access openings. The housing further includes a second opening in fluid communication with the tubing system. The heater also includes a heater tube defining a first end connected to the first opening in the housing. An elongated electrical heating element is at least partly disposed within the outer tube, and has opposite ends extending out of the first end of the heater tube and through the pair of access openings. The electrical heater includes a first compression fitting sealingly connecting the heater tube to the housing at the first opening, and a pair of compression fittings sealingly connect the elongated heating element to the housing at the access openings.
Another aspect of the present invention is an electrical heater including a housing made of a polymer material. The housing has an internal passageway permitting fluid flow through the housing. The heater includes a tube having a first end connected to the housing in fluid communication with the passageway. An elongated metallic electrical heater element has a portion disposed within the tube, and has opposite ends extending out of the first end of the tube. The ends of the heating element have connectors adapted for coupling to an electrical power source. The housing has a first sidewall portion with a first opening therethrough in fluid communication with the passageway. The housing also has a second sidewall portion having a pair of access openings therethrough. The first opening and the pair of access openings each have first and second portions. The first portions have a diameter that is larger than the second portion to form pockets. At least a portion of the first end of the tube is disposed in the first opening, and the opposite ends of the elongated metallic heating element extend through the access openings with the connectors disposed external of the housing. A first resilient ring is disposed in the pocket of the first opening, and a first compression member is operably coupled to the housing to compress the first resilient ring and provide a seal between the tube and the housing. A pair of resilient rings are disposed in the pockets of the access openings, and a second compression member is operably coupled to the housing to compress the pair of resilient rings and provide a seal between the elongated metallic electrical heating element and the housing.
Yet another aspect of the present invention is an electrical heater including a housing made of a polymer material and having an internal passageway providing fluid flow through the housing. The housing has first and second openings to the passageway and at least one access opening open to the passageway. The heater includes an elongated tube having a first end secured to the first opening of the housing. An elongated electrical heating element is at least partially disposed in the elongated tube. The heating element has an end extending through the access opening such that the end is accessible from outside the housing to permit coupling of an electrical line to the end of the heating element. A compression fitting sealingly couples the electrical heating element to the housing at the access opening.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.